Refresh Marketplace icon asset

[Hanjo92]

Replace the current simple flame face icon with a more polished Marketplace icon that communicates Git diff review: flame, Git branch nodes, and review approval/check motif. Update both the SVG source and packaged PNG asset.

[Hanjo92]

Closing after publishing the refreshed icon in v0.0.13.

[Hanjo92]

Replaced the Marketplace icon with a new flame + Git branch + review check design. Packaged and published in hanjo92.git-roast-reviewer v0.0.13.

Marketplace URL: https://marketplace.visualstudio.com/items?itemName=hanjo92.git-roast-reviewer